Device for feeding perforated webs



Jan. 20, 1970 DEAN ETAL 3,499,6$8

DEVICE FOR FEEDING PERFORATED WEBS Filed July 28, 196'? 3 Sheets-Sheet 1 INVENTORS HAROLD L. DEAN ROBERT T. PEARSON A TTORNE Y Jan. 20, 1970 H. L. DEAN ET AL 3,

DEVICE FOR FEEDING PERFORATED WEBS Filed July 28, 1967 3 Sheets-Sheet 2 m m g g 3 8 O w l v v D 1 I fl m m g a z W r co m Jan. 20, 1970 H. DEAN ET AL 3,490,668

DEVICE FOR FEEDING PERFORATED WEBS I Filed July 28, 1967 3 Sheets-Sheet 5 United States Patent O US. Cl. 226-74 9 Claims ABSTRACT OF THE DISCLOSURE An edge perforated web is fed for processing, e.g., printing, by a pair of tractor devices having sprocket pins engaging the web perforations. Each tractor employs an idler belt which is spring biased to press the web against the tractor chain and which is driven by the sprocket pins so that the driving forces are transferred to the web by the friction forces generated at the webbelt and web-chain interfaces and not by contact between the pins and the edges of the perforations. Tearing of the web is thus eliminated. The idler belt of each tractor is mounted thereon by a latchable four-bar linkage to enable easy and rapid loading and unloading of the tractor.

BACKGROUND OF THE INVENTION This invention relates to apparatus for feeding perforated webs and, more particularly, relates to a sprocket drive mechanism for feeding edge-perforated paper forms such as, for example, those which are commonly used to receive print-out data from a computer system.

In feeding edge-perforated webs which undergo rapid acceleration and deceleration cycles during processing, such as paper forms fed through a line printer which steps the forms in start-stop cycles of up to 2000 a minute, the tractor chain type of paper drive sprocket has been widely accepted. This device employs a chain, much like a common bicycle chain, which is carried by a pair of sprocket gears positioned beneath each edge of the perforated web. Each link of the chain carries a sprocket pin and the links and pins are spaced in increments equal to the spacing between edge perforations in the web. Each sprocket pin is therefore adapted to engage an edge perforation and due to the two gear suspension of the chain a number of sprocket pins, usually or 6, simultaneously engage the web. In order to keep the web from riding off of the sprocket pins a slotted hinge plate is generally used to press the web from the side opposite the tractor mechanism. A slot is required in the plate to allow clearance for the tips of the sprocket pins which project through the web perforations.

This type of mechanism has been found to be a great improvement over the simple sprocket wheel since while the wheel can have no more than one or two sprocket pins engaging the web at any time, the tractor chain arrangement has up to five or six pins simultaneously engaging the web. This distributes the driving forces over a greater number of pins and perforations as compared to the sprocket wheel and therefore the tendency to tear the web is greatly lessened. However, the driving forces are still communicated to the web via the internal edges of the perforations, which are of relatively small area, and the web tearing tendencies, although diminished, have not been entirely eliminated. This is particularly true when only one or two part forms are being fed and in the case where only a single pair of tractors, one for each set of marginal web perforations, is employed.

OBJECTS & SUMMARY OF THE INVENTION It is therefore an important object of the invention to provide an improved web feeding tractor that communicates the web driving forces to the surface of the web rather than to the internal edges of the web perforations.

Another object is to provide an improved web feeding tractor wherein sliding contact between the web and the tractor components is reduced.

Still another object is to provide an improved web feeding tractor which is simply constructed, low in cost and facilitates rapid loading and unloading of perforated webs.

In accordance with the principles of the invention, movable pressure means are provided to coact with the portions of the tractor sprocket pins projecting through the web perforations so that the pressure means moves with the tractor chain and in so doing presses the web against the surface of the chain without appreciable sliding contact. The web is thus squeezed between the tractor chain and the pressure means so that driving forces are imparted to the web surface and the tractor sprocket pins engaging the web perforations serve primarily as alignment and registration means and do not directly transmit driving forces to the web. In accordance with another aspect of the invention, the movable web pressure means is suspended in relation to the tractor by a novel spring biasing and releasing mechanism operable on a four-bar linkage principle to enable disengagement of the pressure means from the sprocket pins whereby the web may be simply and rapidly loaded into and unloaded from the tractor drive mechanism. This mechanism is designed to be self-engaging with the tractor sprocket pins after a web loading operation and is therefore adapted for accurate and reliable use by even the most unskilled operator.

These and other objects, features and advantages of the invention will become apparent from the following detailed description of a preferred embodiment thereof, the description being supplemented by drawings as follows:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevation view showing a four tractor web feeding arrangement adapted for use in a high speed line printer.

FIG. 2a is a right side elevation view of one of the left-hand tractors of FIG. 1, illustrating the inventive aspects thereof.

FIG. 2b is a right side elevation view of the tractor shown in FIG. 2a.

FIG. 3a and 3b are left side elevation views of a lefthand tractor of FIG. 1, illustrating the web pressure mechanism in the closed and open positions, respectively.

FIG. 4 is a close-up view, partially sectioned, illustrating the coaction between the pressure belt, the web and the tractor chain during the web driving operation.

DETAILED DESCRIPTION As shown in FIG. 1, a continuous web of forms 1 having marginal rows of perforations 2 and 3 is fed through a processing machine, e.g., a high speed line printer, by four drive tractors 7, 8, 9 and 10. The tractors have sprocket pins engaging the marginal perforations, the left tractors 7 and 8 engaging the left row 2 and the right tractors 9 and 10 engaging the right row 3. Drive motion is imparted to the upper tractors 7 and 9 by a splined shaft 11 which is journalled between machine side frames 5 and 6 and which receives drive rotation from a suitable drive source (not shown) such as a clutch-brake system or a stepping motor.

The lower tractors 8 and 10 are driven by a splined haft 12 receiving drive rotation from the same drive ource. A pair of mounting bars 14 and 16 provide a stale, two point mounting for each tractor. In accordance llth well-known techniques, the four tractors are laterally .djustable on their mounting shafts to provide proper paler tension and to enable accommodation of different vidth forms. Since such adjustment features do not form part of the present invention, further description theref is omitted. An example of such means, however, may e obtained from U.S. Patent 3,006,520 issued to F. R. -Iouse. Also, an example of suitable means for driving the hafts 11 and 12 in accordance with operation of a line rinter may be gleaned from the same patent. It is noted hat when the arrangement shown in FIG. 1 is employed [1 a line printing environment, a row of print hammers :ooperating with a character bearing drum or belt is :ated between the upper and lower pairs of tractors in the general area denoted by arrow 4. However, it is common 0 eliminate, for economy purposes, the lower pair of ractors when a slower printing rate, e.g., 300 lines per minute, is all that is required.

Referring now to FIGS. 2 and 3, the novel tractors of he invention are hereinafter described. The basic tractor rssembly includes a frame member 20 preferably of cast )r stamped construction. A tube 21 is embedded in the Frame to enable slidable mounting thereof on one of the shafts 14 or 16 (FIG. 1). A pair of sprocket gears 27 and 28 (FIG. 3b) are journalled in the frame in bearings 24 and 22, respectively. Gear 27 is connected to an internally splined hub 26 which is adapted for mounting on a splined ;haft 11 or 12 (FIG. 1) to enable transmission of drive rotation to the gear 27. The gears may be made of any suitable lightweight material, but a durable synthetic such as nylon or Delrin is preferred.

A chain 30, constructed much along the lines of the familiar bicycle chain, is wrapped about the gears. Each link of the chain has a fiat tab 32 (FIG. 2b) projecting later ally outwardly and each tab carries a sprocket pin 34 for engaging the marginal perforations of the web. The tabs 32 ride on a low-friction stationary raceway 36 fixed to the frame 20. The upper surface of the raceway is flat so that the sprocket pins are guided in substantially a straight line when they are engaged with the web, thus enabling the web to move in a flat plane. For additional control of the web a guide rail 38 is provided along side of the raceway 36 to insure proper orientation of the web when the pins 34 are being engaged and withdrawn therefrom.

The portion of the tractor thus far described is well known and has been in widespread use on line printers for several years. The novel aspects of the present invention lie in provision of the pressure mechanism 40 which forces the web against the upper surfaces of the moving chain tabs 32. As shown in FIGS. 2a and 2b, a pair of flanged idler pulleys 41 support a belt 42 which has holes 43 spaced to cooperate with the portions of the sprocket pins 34 which project through the web perforations. The pulleys 41 are rotatable about a pair of shafts 46 supported between the side portions of an inverted U-shaped bracket 44. Each pulley has a peripheral groove (not shown) to provide clearance for the tips of the sprocket pins 34 which may project through the belt 42. The bracket 44 is pivotable connected via a pair of parallel pivot arms 49 to a stationary sideplate 48, which is fixed to the frame 20 of the basic tractor by a pair of mounting screws 55 (FIG. 3b). These arms are connected between the shafts 46 and a pair of pins 50 supported in plate 48. A tension spring 52 connected to stud 53 on plate 48 is hooked to the middle of the lower edge of the right-hand (FIG. 2b) side of bracket 44 and biases the whole assembly 40 downwardly toward the chain 30 when the mechanism is in the engaged condition depicted in FIGS. 2a and 2b.

Referring to FIG. 4, it can be appreciated that since the belt 42 is urged downwardly by spring 52 (FIG. 2b) a normal force is set up at the friction interface between the belt 42 and web 1 and at the friction interface between the web and the tabs 32. As the pins 34 accelerate in the feeding direction (to the right) at the beginning of the feeding cycle, these friction forces prevent relative movement between the web and its engaging components and thus the pins do not apply stress to the edges of the web perforations and web tearing is prevented so long as the force of acceleration is less than the highest friction force generated at the two friction interfaces. The web driving forces are thus allocated to the surface of the web and not to the edges of the perforations. Furthermore since the pins 34 engage the leading (right-hand) edges of the belt holes 43 during acceleration, the inertial drag of the pulleys 41 and belt 42 is absorbed by the sprocket pins and does not work against the forces at the friction interfaces.

During deceleration of the pins 34 at the end of the feeding cycle the same friction forces transmit the forces of deceleration to the web and as just described for the acceleration case prevent the pins from exerting a tearing force against the trailing edges of the perforations. If some slight play exists between the pins 34 and the respective trailing edges of the belt and web holes (as illustrated in FIG. 4) due to tolerances or wear, and the inertial drag of the pulleys 41 and belt 42 causes a slippage at one of the friction interfaces, the impact of the'trailing edges of the pins is absorbed by the belt and still prevents tearing of the web.

As is apparent, the force of spring 52 may be varied by an adjustment feature. or the like and different friction materials may be employed on the surfaces of the belt and the tabs 32 to vary the parameters of this interaction depending on the type of web and feeding speeds desired. It is important to note, however, that with the arrangement of the invention the web can be fed at speeds and exposed to acceleration forces a full order of magnitude greater than those possible with the prior art device employing a static retainer plate without encountering web tearing problems.

The assembly 40 is provided with a latching mechanism, best illustrated in FIGS. 3a and 3b, for enabling positive engagement of the mechanism and to permit selective disengagement thereof for rapid and easy loading of a web into the tractors. Since the pivot arms 49 together with the bracket 44 and plate 48 create a four-bar linkage, the assembly 40 can be pivoted away from the chain 30 without upsetting the parallel relationship be tween the lower run of belt 42 and the upper run of chain 30. Engagement of the belt with the pins 34 is therefore accomplished through movement of the belt in a direction substantially parallel with the axes of the pins. This maximizes ease of engagement.

As shown in FIG. 311, wherein the front side of bracket 44 is cut away, the assembly is latched in a closed condition by a latch arm 60 which is pivotable about pin 64 fixed in a mounting block 65 attached to the underside of bracket 44. Latching stud 66 projecting from the side of arm 60 hooks under a finger 68 formed in plate 48. This finger establishes a limit to the upward move-ment of the assembly 40 but due to the recessed portion 69 some amount of downward play is permitted. This prevents the latch mechanism from interferring with the freedom of spring 52 to effect the previously described pressure action on the surface of the web. Due to finger 68, however, the assembly cannot be forced so far upward as to become disengaged from the pins 34 during operation.

To disengage the assembly, the end of arm 60 is manually depressed to cause a counterclockwise pivoting thereof against the bias of compression spring 62. This frees stud 66 from finger 68 and enables the assembly 40 to be pulled upward out of engagement with the sprocket pins. When the assembly is fully opened (FIG. 3b), the spring 52 shifts over-center with respect to arms 49 and acts to keep the assembly open. The right arm 49 and plate 48 abut at point 70 to hold the assembly in this position. The operator is then free to insert a web into the tractor and align it on the sprocket pins.

When the assembly is flipped closed, it makes no difference if the pins 34 do not immediately engage with the holes in belt 42 since as soon as the chain 30 begins its first movement, the pins will fall into the holes and the spring 52 will force the assembly into its correct closed position with the stud 66 hooked under finger 68.

In recapitulation, it can be seen that each edge of the web is firmly pressed between a pressure belt 42 and its set of cooperating tractor tabs 32, thereby causing the driving forces to be; communicated to the web primarily through the surface thereof with a reduced amount of relative movement between the belts 42, web 1 and tabs 32 during the driving action. This virtually eliminates web tearing by distributing the driving forces over a much larger area of the web. Further, the novel pressure belt assembly of the invention, mounted on the above described four-bar mechanism, enables simple, reliable and rapid operation of the device by even the least skilled of operators.

It will be appreciated that various changes in the form and details of the above described preferred embodiment may be effected by persons of ordinary skill without departing from the true spirit and scope of the invention.

We claim:

1. A device for feeding a perforated web, comprising, in combination:

moveable web supporting means;

a plurality of sprocket pins fixed to said web supporting means for engaging plural perforations in said web along a substantially flat section thereof;

a second supporting means contacting the side of said web supporting means opposite said web, said second supporting means maintaining the portion of said web supporting means fixed to sprocket pins engaging said perforations in a fixed substantially straight path; and

pressure means drivingly engaged with the portions of said sprocket pins projecting through said perforations and having traction surfaces bearing against the portions of said web lying between said pins, the friction forces transmitted to said portions of said web from said traction surfaces moving said web when said pressure means is driven by said sprocket pins.

2. The device set forth in claim 1, further comprising:

means for mounting said pressure means in movable relation away from said web supporting means to enable variation in the spacing therebetween.

3. The device set forth in claim 2, further comprising:

a spring biasing said pressure means into engagement with said sprocket pins.

stop means for limiting the freedom of movement of said pressure means away from said web supporting means.

5. The device set forth in claim 4, further comprising:

means for rendering said stop means ineffective to enable disengagement of said pressure means from said sprocket pins.

6. A device for feeding a perforated web comprising,

in combination:

a moveable tractor chain for supporting said web, said tractor chain also supporting a plurality of sprocket pins for engaging perforations in said web along a substantially flat section thereof;

supporting means located on the side of said tractor chain opposite said web, said supporting means maintaining the portions of said tractor chain supporting sprocket pins engaging said perforations in a fixed substantially straight path; and

an idler belt mounted on a side of said web opposite said tractor chain and having spaced holes for engaging pins projecting through said perforations whereby movement of said tractor chain imparts equal movement to said belt, said belt adapted to contact the surface of said web and move said web by the friction forces between said belt and said web.

7. A device for feeding a erforated web comprising,

in combination:

a moveable tractor chain supporting a plurality of sprocket pins for engaging perforations in said web along a substantially flat section thereof;

an idler belt mounted on a side of said web opposite said tractor chain and adapted to contact the surface of said web, said belt having spaced holes for engaging the portions of said sprocket pins projecting through said perforations whereby movement of said tractor chain imparts equal movement to said idler belt;

a pair of freely rotatable pulleys on which said idler belt is mounted;

a U-shaped bracket in which said pair of pulleys are journalled; and

a pair of parallel arms pivotably suspending said bracket to enable movement of said idler belt toward and away from said fiat section of said web without altering the parallel relationship between the pin engaging portion of said belt and said fiat section.

8. The device set forth in claim 7, further comprising:

a spring biasing said U-shaped bracket toward said web, whereby said belt is maintained in engagement with said pins and is pressed against said Web.

9. The device set forth in claim 8, further comprising:

latching means operable when said belt is engaged with said sprocket pins to limit the extent of movement of said U-shaped bracket away from said web, thereby preventing said belt from riding out of engagement with said pins.

References Cited UNITED STATES PATENTS 2,453,031 11/1948 Olds 22674 2,724,254 11/1955 Zanger 226-74 X 3,209,972 10/1965 Benbow 22674 M. HENSON WOOD, JR., Primary Examiner RICHARD A. SCHACHER, Assistant Examiner US. Cl. X.R. 22682, 172 

